Image orthicon focusing coil and field flaring ring



NOV- 24, 1964 JgF. FLEMING ETAL 3,158,774

IMAGE ORTHICON FOCUSING COIL AND FIELD FLARING RING Filed June 8, 1962 otd NAII @mi um E INVENTORS. i'. IL 5MM/G B cK Jn. DAN/5L. C. BY

United States VPatent O 3,158,774'. j A lMAGE RTHKCN FCUSING CQHL AND BEELD FLARING-PJNG n .loel E. Fleming, Bloomington, 1nd., and Daniel C. Buck, Horseheads, NX., assignars," by mesne assignments, to the United States of America as representedby the Secretary ofthe Air Force f* i Filed .lune 8, 1962, Ser. No. 261,224

1 Ciaim. (Cl. S13-w84) The invention relatesfgenerally to focusing of image orthicon tubes, and more particularly to an improvement in the method of focusing' in order to increase its sensitivity and resolution ofthe picture on the photosensitive face plate. k

In order to improve the focusing and sensitivity of the image orthicon, the field from the focus coil should be ared out from the target in the direction toward the photosensitive surface. One proposed method for providing a solution has been to design focusing coils with variable ampere turns per inch along the coil in its axial or Z direction. The lield obtained is the resultant of the superposition of the iields of the various sections of the focus coil having different ampere turns per inch.

The foregoing solution has a number of disadvantages. Firstly, a number of power supplies of different current, voltage and polarity ratings are required in order to supply a coil; and secondly, the magnetic shield normally provided on the outer periphery of the coil tends to average out or smooth out the fields generated by the separate coil sections, thereby leaving a relatively uniform field without the desired liaring at a target-photosensitive surface section ofthe tube.

In order to overcome the above enumerated disadvantages, it is necessary to leave olf the outer shield, thereby subjecting the focusing lield to the effects of the earths magnetic field, or increase the magnetic shield by at least twice its diameter, which, not only Wastes space, but requires major design changes in existing equipment.

This invention provides a solution for the problem without theV disadvantages of the previously mentioned solution. The desired result is achieved by placing either a ring or rings of a high permea'blematerial Within the standard, shielded, focusing coil of a conventional image orthicon' tube arrangement.

Accordingly, it is an object of this invention to provide improved focus for image orthicon tubes. v

` It is another object of this invention to provide improved focus of image orthicon tubes Without requiring redesign of existing equipment. o

It is still another object of this invention to provide an improved focusing of image orthicon tubes without the attendant disadvantages of prior art solutions.

It is a further object of this invention to provide improved focusing in an image orthicon tube by providing for a novel arrangement to control the focusing liuX lines.

It is a still further object of this invention to provide a focusing arrangement for a standard image orthicon tube wherein a ring or rings are inserted within the conventional focus coil to provide a predetermined pattern of the focus flux lines.

An additional object of this invention involves the provision of shunting rings which may be varied in shape, thickness, width, type of material, number of pieces and spacing in order to vary the shape of a magnetic iield from a focus coil. l

These and other advantages, features and objects of the invention will become more apparent from the followt ing description taken in connection with the illustrative embodiment in the accompanying drawing wherein:

FIGURE l is a partially schematic representation of a standard image orthicon tube having a shunting ring of this invention applied thereto;

FIGURES 2 through 5 illustrate in section various shapes and sizes of shunting rings which may be utilized with an image orthicon tube; and Y FIGURE 6 is a plot of a magnetic field strength. against the distance along the focus coil.

Referring to FIGURE l, there is shown an image orthicon 10 which combines the principles o f both image multiplication and signal multiplication while maintaining a relatively high sensitivity. The image orthicon utilizes a photocathode 12 which, when light is projected throughfthe front end of a tube, causes electrons to be releasedtoward the target 14. An electron image is formed on target 14 while the secondary electrons therefrom are drawn away from the iield by means of a target screen 15 located proximate to the target. Withdrawal of the secondary electrons causes corresponding picture elements of the target to become positive to a slight extent. The target structure is enclosed within enlarged portion 16 of envelope 1S which houses the entire target and electron gun structure of the image orthicon. The gun structure is located at the end of the envelope opposite to section 16 and is designated generally as 20. Within the envelope is located a conventional accelerating electrode 22 which is coated on the inner wall of the envelope 18. The purpose of the accelerating electrode 22 is to accelerate an electron beam toward the target 14. A decelerating ring 24, adjacent the gun side of target 14, is used to decelerate the electron beam from the gun structure 20 as it approaches the target 14. A deflection yoke 26 surrounds the neck-down portion of the envelope 18, as shown, and contains the conventional horizontal and vertical deilecting coils Which form part of a conventional scanning system. In addition, a conventional alignment coil 28 is provided adjacent the gun structure while the photoelectrons from the photocathode are focused by the magnetic iield of the long focusing coil 30. A magnetic shield 32 surrounds the coil structure.

The device described thus far operates in thesame manner as a conventional image orthicon such as that described in Televisiom second edition, by Zworykin and Morton, John Wiley and Sons, Inc., New York, publishers. The electron beam 34 approaches the target 14 at a low velocity due to the action of decelerating ring 24. Zero potential at the target area reflects the beam back toward the electron gun 20 while positive portions of the target surface cause electrons from the beam 34 to neutralize the charge, and the beam is then repelled back toward the gun 20 of the image orthicon tube. Thev variation in the electrons provides a modulation of the beam which, upon its return from the target, enters a conventional secondary emission multiplier at the gun end of the tube.

This invention involves the addition of a high permeability material 36 inside the standard shielded focusing coil 30 of the conventional image orthicon of the foregoing description. The rings 36 shunt out part of the solenoid field of the focus coil 3G in order to produce a desired flare out as indicated by the dashed showing of the Vflux lines in FIGURE 1. The shuntingv rings may be was placed in a standard shielded coil. The desired curve varying ony of the parameters affecting the ultimate curve shape.

Although the invention has been described relative to a particular material and use with an image orthicon tube, it should be understood that other high permeability materials may be utilized. In addition, if other configurations of magnetic eld are desired with vacuum tubes such as cathode ray tubes, pickup or camera tubes, the broad invention of placing magnetic shunting rings in a focusing coil would be equally applicable.

We intend to be limited only by the accompanying claim.

We claim:

A television camera tube having a means for producing a beam of electrons at one end of said tube, a photocathode remote from said first-mentioned means at the other end of said tube, a target structure at said other end of said tube and spaced from said photocathode for receiving a charge pattern from said photocathode, means for scanning said beam over said target, means for producing a magnetic field for focusing said beam, said means comprising a solenoid around said tube and extending from said photocathode to said means for producing a beam, and means adjacent the end of said tube containing said photocathode and said target for flaring the magnetic iield from said focus solenoid from said target toward said photocathode, said last-mentioned means comprising a ring of high permeable magnetic material intermediate said solenoid and said picture tube, and extending from said photocathode portion of said tube to said target portion of said tube.

References Cited in the tile of this patent UNITED STATES PATENTS 2,803,770 Harkensee Aug. 20, 1957 

